BEIJING — Chinese banks that do business with North Korea stand to lose several billion dollars in the wake of new United States Treasury Department sanctions on all such foreign institutions, analysts said on Friday.

The new sanctions were announced days before a visit to Beijing by Secretary of the Treasury Jacob J. Lew and Secretary of State John Kerry for an annual meeting on economic and security issues that starts on Monday and whose agenda this year includes North Korea.

The Chinese banks most affected by the sanctions will be comparatively small regional ones that facilitate the bulk of North Korea’s business in China, the analysts said. Major banks in China suspended their North Korean accounts in 2013 after the Chinese president, Xi Jinping, criticized a nuclear test conducted by the North that year, the analysts said.

The Bank of China, for example, which has been expanding its operations in the United States and did not want its American business tainted by cooperation with North Korea, closed the account of North Korea’s most important financial institution, the Foreign Trade Bank, in May 2013.

The smaller banks in the northeast area of China that borders North Korea would probably not want to risk continuing to do business with the North because the cost of sanctions by the United States would far outweigh the benefits of such commercial ties, said Jin Qiangyi, dean of the institute of Northeast Asian Studies at Yanbian University in Yanji.

China is by far North Korea’s biggest trading partner.

Using a provision of the Patriot Act, the Treasury Department designated North Korea on Wednesday as a “primary money-laundering concern,” a move that will enable Washington to take aggressive measures to cut off its access to the United States financial system.

Under the new designation, non-American banks and other entities are banned from conducting dollar transactions on behalf of North Korea, a prohibition intended to crimp the North’s economic activities and its ability to further expand its nuclear program.

The Chinese government said on Thursday that it opposed the Treasury action, although Beijing signed onto a tough new round of United Nations sanctions imposed on North Korea in March as punishment for a nuclear test it conducted earlier this year.

“We consistently oppose imposing unilateral sanctions on other countries based on one’s domestic laws,” said a Foreign Ministry spokeswoman, Hua Chunying. Instead of creating new sanctions, countries should “fully implement” the United Nations sanctions established in March, she said.

The United Nations resolution called on member states to terminate “joint ventures, ownership interests and correspondent banking relationships” with banks in North Korea within 90 days. The Treasury move goes a step further with its prohibition against United States banks’ allowing North Korea access to the American financial system via third-country banks.

If China were committed to enforcing the United Nations sanctions it agreed to, then the Treasury move would not affect it.

The Foreign Ministry spokeswoman’s pointed use of the word “unilateral,” however, raised questions about Beijing’s commitment to the March sanctions.

The tough approach by the Treasury contrasted with the decision by Mr. Xi to meet this week with a senior North Korean envoy, Ri Su-yong. Mr. Ri was dispatched by his country’s young leader, Kim Jong-un, to mend North Korea’s frayed ties with China, but he told the Chinese leader that North Korea had no intention of giving up its nuclear weapons, North Korean state-run media reported.

The Treasury action also came as Mr. Kim has begun a policy, named byungjin, that calls for North Korea to keep expanding its nuclear weapons program while pushing for development that would bolster its rudimentary economy.

The collective impact on the regional Chinese banks by the Treasury action will probably be much greater than the losses incurred by Banco Delta Asia, a bank based in the Chinese special administrative region of Macau, when it was designated a money-laundering concern in 2005 because of its dealings with North Korea, said Cho Bong-Hyn, an analyst at the Industrial Bank of Korea’s Research Institute in Seoul.

The United States froze $24 million in North Korean money held in Banco Delta Asia.

“The impact would amount to approximately a few billion U.S. dollars, considering most of North Korea’s foreign bank accounts are in China,” Mr. Cho said.

Even so, he said, few of these banks are entirely dependent on North Korea’s business. He doubted that many banks had North Korean deposits amounting to more than 10 percent of the bank’s total deposits.

“I don’t think these Chinese banks will be shaken by the said losses,” he said. “They may, however, worry about loss of future transactions.”

Most of them are in the major trading cities of Dandong and Hunchun on the border with North Korea, he said.

These banks will now have to ensure that North Korea does not open bank accounts with them by using conduits.

“If such illegal accounts are detected, it could be fatal for these banks,” he said. “So both Korean and Chinese banks will have to do their best to prevent North Koreans from opening these irregular bank accounts with them.”

The main banks in China were unnerved by what happened to Banco Delta Asia, and by 2013, after a nuclear test by the North earlier that year, they stopped doing business with North Korea, said Andray Abrahamian, associate research director of Choson Exchange, a nonprofit group based in Singapore that provides training for entrepreneurs in Pyongyang, the North Korean capital.

“The writing was already on the wall then,” Mr. Abrahamian said.

Even if a Chinese bank processed transactions for North Koreans in the Chinese currency, the renminbi, that bank’s dollar trade would remain at risk, he said.

It is not clear where North Korea might seek alternative places to conduct financial transactions outside the normal banking systems, the analysts said.

Certainly, North Koreans would want locations far away from financial hubs. Recently, North Korean businesspeople have mentioned Cambodia and Indonesia as possible channels, said a Singaporean analyst who declined to be identified because of the sensitivity of the matter.

Soon after the United Nations sanctions were imposed in March, Chinese traders in Dandong, the main gateway for transportation of Chinese goods into North Korea, were using alternatives to the Chinese-run Bank of Dandong.

In order to receive payments from North Korea, one major trader in Dandong said in April that he would receive a 50-percent down payment before a shipment. The money would be deposited in the Dandong office of the Korea Kwangson bank.

That bank is North Korean and does business out of unmarked offices on the 13th floor of an office tower on the banks of the Yalu River. It was described as the last North Korean bank operating in the city.

The trader would pick up the remaining 50 percent payment once the goods arrived in North Korea, he said. The transactions would usually be in renminbi, although sometimes they were in dollars, he said.

In March, the Treasury singled out the Korea Kwansong bank for using front companies to gain access to the United States financial system and process transactions that supported weapons of mass destruction and ballistic missiles.

Previously, the Treasury had said that North Korean leaders had used one of the bank’s front companies to open accounts at a major Chinese bank under the names of Chinese citizens and to deposit millions of dollars in 2013.

Su-Hyun Lee contributed reporting from Seoul, South Korea, and Yufan Huang contributed research from Beijing.

A version of this article appears in print on , on Page A3 of the New York edition with the headline: Chinese Banks Brace for U.S. Sanctions on North Korea. Order Reprints | Today’s Paper | Subscribe